1. Field of the Invention
The present invention relates to "door" assemblies which may be rapidly and easily installed over access openings, such as manways which are provided in the vessels of steam generators in a nuclear power plant, after removal of the covers from such access openings pursuant to a maintenance and/or inspection procedure. More specifically, this invention is directed to radiation reducing "door" assemblies which enable tools and/or electrical cables to extend through the access opening with which the "door" assembly is temporarily associated and particularly to radiation reducing "door" assemblies which, even with a tool and/or cables entering the steam generator therethrough, minimize the exposure to radioactivity of service personnel performing maintenance on the steam generator of a nuclear power system. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
2. Description of the Prior Art
For a description of the problem to which the present invention is directed, and an example of a prior solution to that problem, reference may be had to U.S. Pat. No. 4,801,423 which is assigned to the assignee of the present invention. The radiation shielding door assembly of the referenced patent has many attributes which are shared by the present invention. The door assembly of the referenced patent is intended for use with tools which are installed in the steam generator and subsequently remotely controlled via cables which extend over the lip of the steam generator access opening via a gap which is left between the door assembly and the wall of the steam generator. In other words, the radiation shielding door assembly of the referenced patent, as shown in FIGS. 2 and 3 thereof, prevents any line-of-sight "streaming" of radiation out of the steam generator.
It has been found, in many instances, that it is necessary or desirable to employ tool manipulators in the course of performing maintenance and/or inspection procedures on a steam generator. These tool manipulators include elongated, articulated arms which extend into the interior of the steam generator through the access opening and are actuated to position tools at any selected location on the tube sheet of the steam generator. Such tool manipulators may be mounted on the flange which defines the steam generator vessel manway and have the capability of extending their distal ends back out through the manway opening. This permits tools and other material to be delivered into the steam generator and also to be retrieved therefrom, for example for the purpose of tool changing, without dismounting of the tool manipulator from the steam generator. In order to accommodate such tool manipulators, a radiation shielding door assembly which does not completely obscure the line-of-sight between the interior and exterior of the steam generator via the manway opening must be provided. Such a door assembly must not interfere with the mounting of the manipulator and must have the capability to establish a substantially air-tight seal about the manway opening when the tool manipulator is removed.